Cooling fan

ABSTRACT

A cooling fan includes a fan housing ( 30 ) having a central tube ( 34 ) extending upwardly thereof, a bearing ( 60 ) received in the central tube, a stator ( 20 ) mounted around the central tube, a rotor ( 10 ) including a hub ( 12 ) having a shaft ( 18 ) extending from the hub into the bearing, and a oil retaining ring ( 40 ) mounted around the shaft. A slot ( 180 ) is defined in a top end ( 182 ) of the shaft of the rotor near the hub to prevent the escaping oil from continuously creeping out along the shaft. The slot is located between the retaining ring and the bearing. The bearing has a plurality of channels ( 68 ) defined in an outer surface thereof, for guiding the escaping oil to return to an oil reservoir defined in a bottom of the central tube.

FIELD OF THE INVENTION

The present invention relates to a cooling fan, and more particularly relates to a cooling fan which has a motor with a bearing having good lubricating characteristics.

DESCRIPTION OF RELATED ART

With the continuing development of the electronic technology, electronic packages such as CPUs (central processing units) are generating more and more heat that is required immediate dissipation. Cooling fans are commonly used in combination with heat sinks for cooling CPUs. Cooling fan performance mostly depends on performance characteristics of bearings used. Good lubricating qualities of the bearings increases the life-span of the bearings.

Referring to FIG. 5, a conventional cooling fan comprises a rotor 1 having a shaft 2 extending downwardly from a central portion of the rotor 1, a bearing 3 defining an inner hole for receiving the shaft 2 therein, and a frame 4. A central tube 5 extends upwardly from a middle portion of the frame 4 and defines a through hole 7 therein. The bearing 3 impregnated with lubricant oil is secured in the through hole 7 of the central tube 5 to rotatably support the rotor 1. An oil retaining ring 6 is mounted around the shaft 2 and located above a top end of the bearing 3 when the cooling fan is assembled. A gap is defined between a circumferential surface of the oil retaining ring 6 and an inner circumference of a top end of the central tube 5. During operation of the cooling fan, the oil originating from the bearing 3 passes out through the gap and is lost. Lubrication of the bearing 3 is thus gradually diminished. The friction between the shaft 2 and the bearing 3 increases, resulting in noise or malfunctioning. Finally the performance of the cooling fan is reduced, and the life-span is resultingly shortened.

What is needed, therefore, is a cooling fan which can reduce or eliminate lubricant oil loss.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a cooling fan comprises a fan housing having a central tube extending upwardly thereof, a bearing received in the central tube, a stator mounted around the central tube, and a rotor including a hub having a shaft extending from the hub into the bearing. A slot is defined in a top end of the rotor near the hub. An oil retaining ring is mounted around the shaft and located above the slot of the shaft. An oil buffer is defined between the retaining ring and the bearing and communicates with the slot of the shaft. During operation of the cooling fan, the slot of the shaft prevents the escaping oil keep creeping out along the shaft. The escaping oil is received in the buffer and then flows back to an oil reservoir in a bottom of the central tube through channels defined in an outer surface of the bearing. Thus the oil can be kept from leaking out of the bearing. Good lubricating quality of the bearing and shaft is consistently maintained, thereby improving the quality and life-span of the cooling fan.

Other advantages and novel features of the present invention will be drawn from the following detailed description of the preferred embodiments of the present invention with attached drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present cooling fan can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present cooling fan. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is an isometric, exploded view of a cooling fan in accordance with a preferred embodiment of the present invention;

FIG. 2 is an isometric, assembled view of the cooling fan of FIG. 1;

FIG. 3 is a cross sectional view of the cooling fan taken from line III-III of FIG. 2;

FIG. 4 is an enlarged view of a bearing of the cooling fan of FIG. 1; and

FIG. 5 is a cross sectional view of a conventional cooling fan.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 through 4, a cooling fan according to a preferred embodiment includes a rotor 10, a stator 20 in respective to which the rotor 10 is rotatable, a fan housing 30 receiving the rotor 10 and the stator 20 therein, and an oil retaining ring 40 mounted in the fan housing 30.

The fan housing 30 comprises a base 32 and a central tube 34 extending upwardly from a central portion of the base 32. The central tube 34 defines a central hole 36 therein and forms an open end at a top portion thereof. An annular recess 38 is formed on an inner circumference of the top portion of the central tube 34. The recess 38 communicates with the central hole 36. Thus the top portion of the central tube 34 has an inner diameter larger than that of the other portion of the central tube 34.

The rotor 10 comprises a hub 12 forming a shaft seat 120 at a central portion thereof, a plurality of fan blades 14 extends radially from an outer periphery of the hub 12, a magnet 16 adhered to an inner surface of the hub 12, and a shaft 18 received in the shaft seat 120 extending downwardly from a central portion of the shaft seat 120. The shaft 18 defines an annular slot 180 in a circular circumference thereof, near a top end 182 adjacent to the hub 12. An annular notch 184 is defined near a free end 186 of the shaft 18 far from the hub 12. An annular protrusion 19 around the shaft seat 120 extends downwardly from the hub 12. The protrusion 19 has an outer diameter smaller than the inner diameter of the top portion of the central tube 34. The protrusion 19 and the shaft seat 120 cooperatively define an annular chamber 190 therebetween.

The stator 20 includes a stator core 22 consisting of layered yokes, stator coils 24 wound on the stator core 22 to establish an alternating magnetic field, and a PCB (Printed Circuit Board) 26 electrically connected with the stator coils 24. To avoid the coils 24 coming into electrical contact with the stator core 22, upper and lower insulating frames 28 are used to cover the stator core 22 and electrically insulate the stator coils 24 from the stator core 22.

The oil retaining ring 40 has an outer diameter approximately the same as the inner diameter of the top portion of the central tube 34 which defines the recess 38 therein. Thus the retaining ring 40 is received in the recess 38 and substantially encloses the open end of the central tube 34 when the cooling fan is assembled. The retaining ring 40 defines a mounting hole 42 in a middle portion for extension of the shaft 18 therethrough. The mounting hole 42 of the retaining ring 40 has a diameter approximately the same as or a little larger than the diameter of the shaft 18. In this embodiment, the diameter of the mounting hole 42 of the retaining ring 40 is larger than the diameter of the shaft 18. A narrow gap 44 with a width about 0.2 mm (Millimeter) is defined between an inner circumferential surface of the retaining ring 40 and an outer surface of the shaft 18. The gap 44 thus can avoid friction generated between the retaining ring 40 and the shaft 18 during operation of the cooling fan.

The cooling fan further includes a bearing 60 mounted in the central hole 36 of the central tube 34 via the open end. The bearing 60 defines an axial hole 62 therein for extension of the shaft 18 therethrough. The axial hole 62 of a middle portion of the bearing 60 has a diameter larger than that of two opposite ends (i.e. top and bottom ends 64, 65) of the bearing 60. Therefore a space 70 is defined between the middle portion of the bearing 60 and the shaft 18 when the fan is assembled. This space 70 can improve the supply of lubrication oil to the bearing 60. On the other hand, the middle portion of the bearing 60 is spaced from the shaft 18, whilst only the two ends 64, 65 of the bearing 60 contact with the shaft 18. The contacting area between the bearing 60 and the shaft 18 is thus reduced, thereby reducing the friction generated between the bearing 60 and the shaft 18. For reducing oil loss of the cooling fan, each of the two ends 64, 65 of the bearing 60 and the shaft 18 form a clearance of only 0.002˜0.005 mm. A chamfer angle is formed at each of the ends 64, 65 of the bearing 60 for facilitating mounting of the bearing 60 in the central hole 36 of the central tube 34.

A plurality of channels 68 are defined in an outer surface of the bearing 60 for flowing back of the lubricant oil. The channels 68 communicate with the axial hole 62 of the bearing 60. Each of the channels 68 includes a first portion 680 defined in a top and a bottom end surfaces 640 of the two ends 64, 65 and a second portion 682 defined in an outside surface 66 of the bearing 60. The first portion 680 of the each channel 68 is curve shaped. In a vertical view, the first portion 680 of the top end surface 640 extends outwardly from the axial hole 62 to the outside surface 66 of the bearing 60 along an anti-clockwise direction as the rotation direction of the cooling fan. Alternatively, the first portion 680 of the channel 68 can extend along a clockwise corresponding to the rotation direction of the cooling fan when the cooling fan is rotated clockwise. The channels 68 can guide the leaking oil to return back to an oil reservoir (not labeled) defined in a bottom of the central tube 34.

When assembly, the stator 20 is mounted around the central tube 34. The bearing 60 is received in the central hole 36 of the central tube 34. The top end 64 of the bearing 60 is lower than the top portion of the central tube 34. The shaft 18 extends through the axial hole 62 of the bearing 60 and thus rotatably engages with the bearing 60. The stator 20, the rotor 10, the central tube 34, the oil retaining ring 40 and the bearing 60 construct a motor for the cooling fan. The slot 180 of the shaft 18 is located above the top end 64 of the bearing 60. The retaining ring 40 is received in the recess 38 of the top portion of the central tube 34 and is located above the slot 180 of the shaft 18. Thus the retaining ring 40 and the bearing 60 are located at two opposite sides of the slot 180. An oil buffer 50 is defined between the retaining ring 40 and the bearing 60. The oil buffer 50 communicates with the slot 180 of the shaft 18. A locking washer 80 is located between the bottom end 65 of the bearing 60 and the central tube 34. The locking washer 80 defines an inner hole 82 therein. The inner hole 82 has a diameter smaller than the diameter of the shaft 18, but larger than the diameter of the portion of the shaft 18 defining the notch 184. Thus the locking washer 80 is engaged in the notch 184 to limit movement of the shaft 18 along an axial direction thereof. A wear pad 90 made of high abrasion resistant material is mounted in a bottom end of the central hole 36 of the central tube 34 to face and supportively engage the free end 186 of the rotary shaft 18.

During operation, the rotor 10 is driven to rotate by the interaction of the alternating magnetic field established by the stator 20 and the magnetic field of the rotor 10. Due to the precision clearance formed between the two opposite ends of the bearing 60 and the shaft 18, the bearing 60 enables the cooling fan to run smoothly, stably and with less vibration. The lubrication oil creeps up along the rotating shaft 18 under the influence of the centrifugal force generated by the rotation of the shaft 18 and then escapes to the oil buffer 50 through the clearance defined between the top end 64 of the bearing 60 and the shaft 18. The slot 180 of the shaft 18 prevents the oil from continuously creeping up along the shaft 18. The retaining ring 40 can sufficiently prevent the oil from leaking out of the narrow gap 44. Thus the escaping oil is received in the buffer 50 and then flows back to the bearing 60 through the channel 68 of the bearing 60. Therefore the oil can be kept from leaking out of the bearing 60. Good lubrication of the bearing 60 and shaft 18 is thus consistently maintained, thereby improving the quality and life-span of the cooling fan.

It is understood that the invention may be embodied in other forms without departing from the spirit thereof. Thus, the present example and embodiment are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein. 

1. A cooling fan comprising: a fan housing having a central tube extending upwardly therefrom; a bearing received in the central tube, an axial hole being defined in the bearing; a stator mounted around the central tube; a rotor comprising a hub having a shaft extending from the hub into the axial hole of the bearing, a slot being defined in a top end of the shaft near the hub; and an oil retaining ring mounted around the shaft and located above the slot of the shaft.
 2. The cooling fan as claimed in claim 1, wherein a recess is defined in a top portion of the central tube receiving the retaining ring therein.
 3. The cooling fan as claimed in claim 2, wherein a gap is defined between an inner circumferential surface of the retaining ring and the shaft.
 4. The cooling fan as claimed in claim 3, wherein the gap has a width not larger than 0.2 mm.
 5. The cooling fan as claimed in claim 1, wherein a middle portion of the bearing has an inner diameter larger than that of two ends of the bearing, a space is defined between the middle portion of the bearing and the shaft.
 6. The cooling fan as claimed in claim 5, wherein a clearance of 0.002˜0.005 mm is formed between each of the two ends of the bearing and the shaft.
 7. The cooling fan as claimed in claim 1, wherein at least one channel communicating with the axial hole of the bearing is defined in an outer surface of the bearing, the at least one channel comprises a first portion defined in top and bottom end surfaces of the ends of the bearing and a second portion defined in an outside circumferential surface of the bearing.
 8. The cooling fan device as claimed in claim 7, wherein the first portion of the at least one channel located at the top surface of the bearings extends outwardly from the axial hole to the outside circumferential surface of the bearing along a rotation direction of the cooling fan.
 9. The cooling fan as claimed in claim 1, wherein an oil buffer is defined between the retaining ring and the bearing, and communicates with the slot.
 10. The cooling fan as claimed in claim 1, wherein the hub forms a shaft seat receiving the top end of the shaft therein, an annular protrusion around the shaft seat extends downwardly from the hub, the protrusion and the shaft seat cooperatively define an annular chamber therebetween.
 11. A cooling fan, comprising: a fan housing having a central tube extending upwardly therefrom, the tube having an open top end; a bearing received in the central tube via the open top end; an oil retaining ring mounted to and substantially enclosing the open top end, the oil retaining ring being spaced from the bearing to form an oil buffer therebetween; a stator mounted around the central tube; and a rotor having a shaft rotatably engaging with the bearing and rotating which magnetically interacts with the stator.
 12. The cooling fan as claimed in claim 11, wherein a slot is defined in the shaft and located between the bearing and the retaining ring.
 13. The cooling fan as claimed in claim 11, wherein the bearing includes a middle portion and two ends, at least one channel communicating with the axial hole of the bearing is defined in an outer surface of the bearing, the at least one channel comprises a first portion defined in top and bottom end surfaces of the ends and a second portion defined in an outside surface of the bearing, the first portion of the channel located at the top surface of the bearing extends outwardly from the axial hole to the outside surface of the bearing along a rotation direction of the cooling fan.
 14. The cooling fan as claimed in claim 13, wherein an inner diameter of the middle portion is larger than that of the ends of the bearing, a space is defined between the middle portion of the bearing and the shaft.
 15. The cooling fan as claimed in claim 13, wherein a clearance of 0.002˜0.005 mm is defined between each of the two ends of the bearing and the shaft.
 16. The cooling fan as claimed in claim 11, wherein a gap is defined between an inner circumferential surface of the retaining ring and the shaft, the gap has a width not larger than 0.2 mm.
 17. A motor comprising: a tube; a bearing received in the tube; a stator mounted around the tube; and a rotor having a shaft extending into the bearing via a top end of the tube and rotatable in respect to the bearing by a magnetic interaction between the stator and the rotor, the shaft having an annular slot defined in a circular circumference thereof, the annular slot being located between the top end of the tube and the bearing; and an oil retaining ring secured to the top end of the tube, the shaft extending through the oil retaining ring.
 18. The motor as claimed in claim 17, wherein the bearing has an axial hole receiving the shaft of the rotor therein, a diameter of the axial hole is smaller at top and bottom end portions of the bearing than that at a middle portion of the bearing.
 19. The motor as claimed in claim 18, wherein a channel is defined in an outer surface of the bearing, the channel communicates top and bottom ends of the axial hole.
 20. The motor as claimed in claim 19, wherein the rotor has a hub, the shaft extends from the hub, the hub has fan blades radially outwardly extending therefrom. 